1. Field of the Invention
The present invention relates to an articulated robot mainly intended for industrial use.
2. Background Art
Polar coordinate articulated robots are often used as industrial robots. FIG. 8 shows one example thereof, which comprises a first arm 1 swingably attached to a base 3, a second arm 2 swingably attached to the tip of the first arm 1, and a multidirectional wrist mechanism 4 attached to the tip of the second arm. A necessary tool hand such as a welding gun or a gripper is mounted on the tip of the wrist mechanism 4 to perform robotic operations.
Patent Document 1 (JP Patent Publication (Kokai) No. 63-288690 A (1988)) discloses an example of the wrist mechanism, which comprises a central cylindrical body and a first and a second end cylindrical body provided at each end thereof. These three members are rotatably connected to each other such that the axes of the individual cylindrical bodies are perpendicular to each other, a rotary member at the tip of the second end cylindrical body is brought to a desired position in a three-dimensional space by rotating the individual members relative to one another. The cylindrical bodies can be rotated relative to one another via a transmission shaft and a gear transmission mechanism, the base end portion of the transmission shaft being connected to the motor as a drive source. As another example of the wrist mechanism, Patent Document 2 (JP Utility Model Publication (Kokai) No. 6-21882 U (1994)) discloses a self-contained two-axis wrist mechanism, which accommodates two motors as drive sources in a power housing.
[Patent Document 1]
JP Patent Publication (Kokai) No. 63-288690 A (1988)
[Patent Document 2]
JP Utility Model Publication (Kokai) No. 6-21882 U (1994)
The conventional robot shown in FIG. 8 is designed to ensure an operating range thereof using the lengths of the first and second arms. Since the number of joints from the base to the wrist mechanism 4 is small, the dead space attributable to bending movements of the first and second arms tends to be larger in the operating area close to the robot. Therefore, it is difficult to arrange a plurality of robots close to each other, and therefore the environment in which the robot can be used is limited.
Compact wrist mechanisms are thus known as disclosed in the above publications. However, they do not function as a robot by themselves and require a long arm. In the example described in JP Patent Publication (Kokai) No. 63-288690 A (1988), in particular, where the three cylindrical bodies are adapted to relatively rotate via transmission shafts and gear transmission mechanism, motive power is transmitted from a single motor as a drive source to all the drive shafts and, as a result, the mechanism is complicated.